The present invention generally relates to antennas, and relates in particular to antenna systems that provide adjustment of reception and transmission field shapes associated with the antenna systems.
Monopole antennas typically include a single pole that may include additional elements with the pole. Non-monopole antennas generally include antenna structures that form two or three dimensional shapes such as diamonds, squares, circles etc. Monopole antennas typically produce a transmission field (and are characterized as having a reception field) that radiates in two adjacent generally circular or elipto-spherical shapes that are joined at the antenna.
Multiple antenna structures produce a wide variety of transmission fields (and corresponding reception fields) according to the physical layout of the antennas and/or transmission signal phase modulations placed on signals that are directed to or received by each of the antennas in an antenna structure. For example, as disclosed in “A Primer on Digital Bean forming” by Toby Haynes, http://www.spectrumsignal.com, Spectral Signal Processing, Mar. 26, 1998, beam shaping antenna structures may be provided by positioning adjacent monopole antennas a distance apart of about ½λ in a linear direction wherein the wavelength is the center wavelength of the signal being either transmitted or received. Beam shaping may also be provided by using a plurality of monopole antennas that are fed electronically through a phase multiplexer and are also each about ½λ apart. As further disclosed in this reference, however, certain wireless transmission systems, such as cellular telephones, operate at a wavelength of 35 cm, while FM radio operates at a wavelength of 3 meters and AM radio operates at a wavelength of 300 meters. Providing beam shaping for such wireless systems clearly requires a not insubstantial antenna area or integrated circuit real estate.
Beam shaping in such wireless transmission systems may have significant value in myriad applications. For example, shaping radio frequency interrogation beams in medical imaging systems, such as magnetic resonance imaging (MRI) systems, may be very beneficial to providing more targeted interrogation MRI fields within a patient, and in other applications, such systems may have a wide variety of applications in monitoring devices such as, for example, tire monitoring devices in automobiles. U.S. Patent Application Publication No. 2007/0159315, for example, discloses a tire pressure monitoring system that employs a fixed antenna array to detect signals from each of four tires using shaped beams.
As wireless communication systems become more ubiquitous, the need for smaller and more efficient antennas systems increases, and in particular for antenna system that provide beam shaping without requiring a large amount of antenna volume or integrated circuit real estate.
There is a need, therefore, for more efficient and cost effective implementation of a antenna systems that provide selectively highly directional beam shaping.